Backup system for operation system in communications system

ABSTRACT

When a network element (NE) detects a trouble in an operation system (OpS) for operating the NE itself, a representative NE is determined among a plurality of NEs operated by this OpS. The representative NE selects a substitute OpS from other OpSs and transmits a request for operating the plurality of NEs to the substitute OpS. Thereafter, the plurality of NEs come under the operation of the substitute OpS. The substitute OpS operates the plurality of NEs based on the operation request.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a backup system for an operationsystem in a communications system in which network elements (NEs) and aplurality of operation systems (OpSs) for operating the NEs, areconnected to each other via a network.

[0003] 2. Description of the Related Art

[0004] There has hitherto been a communications system in which at leastone NE and a plurality of OpSs for operating the NE are connected toeach other via the network. In this communications system, the followingmethods are adopted for monitoring a normality of the OpS itself.

[0005] (1) A host OpS for monitoring the OpSs is installed in thecommunications system.

[0006] (2) The OpSs monitor each other.

[0007] The method (1) or (2) being adopted, if a trouble occurs in acertain OpS in the communications system, the host OpS or other OpS as asubstitute for the OpS with the trouble occurred operates the NEs. Thecommunications system is thereby operated with stability.

[0008] There arise the following problems inherent in the prior art. Ifthe method (1) is adopted, the host OpS and other device must beinstalled in the communications system, and this configuration leads toa rise in operating cost for the communications system. Further, if themethod (2) is adopted, a load on the OpS increases, with the result thata performance of the OpS declines.

SUMMARY OF THE INVENTION

[0009] It is a primary object of the present invention to provide abackup system for an operation system in a communications systemincluding network elements (Network Elements) and a plurality ofoperation systems, which has no necessity of further providing a systemfor monitoring the operation systems and is capable of restraining arise in load upon the operation system.

[0010] To accomplish the above object of the present invention,according to one aspect of the present invention, a backup system for anoperation system in a communications system, comprising: a plurality ofoperation systems connected to each other via a network; and a pluralityof network elements operated by the plurality of operation systems,wherein each of the operation systems operates at least one of theplurality of network elements, each of the network elements monitors theoperation system that operates the network element itself and detectsfailures in this operation system, when the failures are detected, ifthe failures-detected operation system operates a plurality of networkelements, a representative network element is determined among theplurality of network elements under the failures-detected operationsystem, the representative network element selects a substituteoperation system among the other operation systems and transmits anoperation request to the substitute operation system, and each of theoperation systems, when receiving the operation request, as thesubstitute operation system, operates the plurality of network elementsunder the failures-detected operation system.

[0011] According to the present invention, in the communications systemincluding the NEs and the plurality of operation systems, there is nonecessity of further providing the system for monitoring the operationsystems, and the rise of load on the OpS can be restrained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a diagram showing an example of system architecture of acommunications system in an embodiment of the present invention;

[0013]FIG. 2 is a sequence diagram showing how an OpS controls NEs;

[0014]FIG. 3 is a sequence diagram showing how the OpS monitors the NEs;

[0015]FIG. 4 is a sequence diagram showing how the NE monitors the OpS;

[0016]FIG. 5 is an explanatory diagram showing an operational example(synchronization of DBs) in the communications system shown in FIG. 1;

[0017]FIG. 6 is an explanatory sequence diagram showing thesynchronization of the DBs in the communications system shown in FIG. 1;

[0018]FIG. 7 is an explanatory sequence diagram showing how a troubleoccurs in the OpS in the communications system shown in FIG. 1;

[0019]FIG. 8 is a sequence diagram showing an operational example of a(backup) process when the trouble occurs in the OpS in thecommunications system shown in FIG. 1;

[0020]FIG. 9 is a sequence diagram showing an example of a process ofdetermining a first representative NE shown in FIG. 8;

[0021]FIG. 10A is an explanatory diagram showing a broadcast frame; FIG.10B is an explanatory diagram showing an example of a broadcast responseframe;

[0022]FIG. 11 is a flowchart showing an example of a process ofselecting a substitute OpS shown in FIG. 8;

[0023]FIG. 12 is a sequence diagram showing an example of an OpSconnection change process shown in FIG. 8;

[0024]FIG. 13 is a sequence diagram showing an operational example of a(DB restoration) process when the OpS recovers from the trouble in thecommunications system shown in FIG. 1;

[0025]FIG. 14 is a sequence diagram showing an example of a process ofdetermining a second representative NE shown in FIG. 13;

[0026]FIG.15A is an explanatory diagram showing the broadcast frame;FIG. 15B is an explanatory diagram showing an example of the broadcastresponse frame;

[0027]FIG. 16 is a flowchart showing an example of a process ofselecting a restoration-assigned OpS shown in FIG. 13;

[0028]FIG. 17 is a sequence diagram showing an example of an OpSconnection change process shown in FIG. 13; and

[0029]FIG. 18 is an explanatory sequence diagram showing anotherembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Embodiments of the present invention will hereinafter bedescribed with reference to the accompanying drawings. An architectureof each embodiment is exemplification, and the present invention is notlimited to the range of the architectures of the embodiments.

[0031]FIG. 1 is a diagram showing a system architecture of acommunications system 100 in the embodiment of the present invention.The communications system 100 is configured by physically connecting aplurality of network elements (NEs) (which are generally termed“communications devices” and a plurality of operation systems(OpSs)(which are generally termed “management or administrationsystems”) via a communications line (network), wherein a plurality ofblocks 1, 2, 3, 4 are logically segmented.

[0032] The blocks 1, 2, 3, 4 are defined as logical groups eachconsisting of the OpS and at least one network element NE underoperation of this OpS. For instance, the block 1 includes a plurality(e.g., three pieces) of NEs 1-1. 1-2, 1-3 and an operation system OpS10. The OpS 10 contains a plurality of databases (DBs) 11, 21, 31, 41.Each of the blocks 2, 3, 4 has the same configuration as the block 1,and the OpSs and NEs belonging to the blocks 1, 2, 3, 4 have the sameconfigurations.

[0033] Each of the NEs 1-1, 1-2, 1-3 may be defined as a transmissiondevice or a switch for executing a variety of communications-orientedprocesses. The variety of processes is, for example, line setting (linecontrol, switch control), device setting, and trouble shooting of the NEitself and/or the line. Processors (a CPU, an MPU and so forth)incorporated into the NE executes programs, thereby actualizing theseprocesses.

[0034] The OpS 10 is defined as an operation system implementing acommunications function of operating (controlling and monitoring) theNEs 1-1, 1-2, 1-3. The OpS 10 includes a processor (a CPU) and a memory,and the CPU executes programs, thereby actualizing functions ofoperating (controlling and monitoring) the NEs. The database DB 11retains (is stored with) pieces of information (control information) forcontrolling the NEs 1-1, 1-2, 1-3.

[0035]FIG. 2 is a sequence diagram showing an operation when the OpS 10controls a certain NE. Referring to FIG. 2, the OpS 10, when controllinga certain NE, reads the control information for controlling this NE fromthe DB 11, then generates a frame (a control frame) containing thereadout control information, and transmits the generated frame to theabove NE (step S1).

[0036] This NE, when receiving the control frame, executes apredetermined process based on the information contained in this controlframe (step S2). The predetermined process is, for instance, linesetting.

[0037] Thereafter, this NE generates a frame (a response frame)containing result information indicating processing/control results, andtransmits this response frame to the OpS 10 (step S3).

[0038] The OpS 10, when receiving the response frame from the NE,updates the DB 11 on the basis of the result information contained inthe response frame (step S4). With this processing, the DB 11accumulates records of the processing/control results of the NEs 1-1,1-2, 1-3.

[0039] Further, the OpS 10 collects pieces of alarm information from theNEs 1-1, 1-2, 1-3. FIG. 3 is a sequence diagram showing an operationwhen a certain NE troubleshoots (detects a trouble of) the NE itself.

[0040] Referring to FIG. 3, a certain NE, upon troubleshooting, gives analarm (step S5). Next, this NE generates an alarm frame containing alarminformation, and transmits the alarm frame to the OpS 10 (step S6).

[0041] The OpS 10, when receiving the alarm frame from the NE, updatesthe DB 11 based on the alarm information contained in the alarm frame(step S7). With this processing, the DB 11 accumulates records of thealarms (troubles or failures) occurred in the NEs 1-1, 1-2, 1-3.

[0042] Thus, the DB 11 accumulates, as information (first blockinformation) on the operation of NEs of the block 1, the controlinformation of the NEs 1-1, 1-2, 1-3, and information (obtained by theOpS's operating the operation target NEs of the OpS itself) based on theresult information and the alarm information transmitted from the NEs1-1, 1-2, 1-3.

[0043] Further, the OpS 10 receives information (second blockinformation) on the operation of the NEs belonging to the block 2 viathe communications line L from the OpS 20, and stores the DB 21 with thesecond block information. The DB 21 accumulates the second blockinformation.

[0044] The second block information contains the control informationused for the OpS 20 to control the NEs 2-1, 2-2, 2-3 within the block 2,and information (obtained by the OpS's operating the operation targetNEs of the OpS itself) with which the OpS 20 stores the DB 22 on thebasis of the result information and the alarm information received fromthe NEs 2-1, 2-2, 2-3.

[0045] Further, the OpS 10 receives information (third blockinformation) on the operation of the NEs belonging to the block 3 viathe communications line L from the OpS 30, and stores the DB 31 with thethird block information. The DB 31 accumulates the third blockinformation.

[0046] The third block information contains the control information usedfor the OpS 30 to control the NEs 3-1, 3-2, 3-3 within the block 3, andinformation (obtained by the OpS's operating the operation target NEs ofthe OpS itself) with which the OpS 30 stores the DB 33 on the basis ofthe result information and the alarm information received from the NEs3-1, 3-2, 3-3.

[0047] Moreover, the OpS 10 receives fourth block information via thecommunications line L from the OpS 40, and stores the DB 41 with thefourth block information. The DB 41 accumulates the fourth blockinformation.

[0048] The fourth block information is the control information used forthe OpS 40 to control the NEs 4-1, 4-2, 4-3 within the block 4, and isinformation (obtained by the OpS's operating the operation target NEs ofthe OpS itself) with which the OpS 40 stores the DB 44 on the basis ofthe result information and the alarm information received from the NEs4-1, 4-2, 4-3.

[0049] Accordingly, the DBs 11, 12, 13, 14 respectively accumulate thefirst block information. The DBs 21, 22, 23, 24 respectively accumulatethe second block information. The DBs 31, 32, 33, 34 respectivelyaccumulate the third block information. The DBs 41, 42, 43, 44respectively accumulate the fourth block information. Thus, the OpSs 10,20, 30, 40 have (incorporate) the plurality of databases correspondingrespectively to the plurality of OpSs, and the plurality of databasesaccumulate the first through fourth block information corresponding tothe OpSs 10, 20, 30, 40.

[0050] Each of the OpSs 10, 20, 30, 40, when updating the DBcorresponding to the OpS itself, transfers a difference (differenceinformation) occurring due to this updating to other OpSs. For instance,the OpS 10, if the DB 11 is updated as the DB corresponding to the OpS10 itself, transfers a difference in contents accumulated in the DB thatoccurs due to this updating, to other OpSs 20, 30, 40.

[0051] Other OpSs 20, 30, 40 update the DBs corresponding thereto by useof the difference information received from the OpS 10. The contentsaccumulated in the plurality of DBs of the blocks 1, 2, 3, 4 are therebysynchronized.

[0052] Further, in each of the blocks 1, 2, 3, 4, the plurality of NEsperiodically transmits a monitor frame (a monitor message) to the OpSinstalled in the same block, and receives a response frame (a responsemessage) to the monitor frame from the OpS. With this operation, each NEmonitors whether the OpS concerned functions normally (see FIG. 4).

[0053] For example, referring to FIG. 4, the NEs 1-1, 1-2, 1-3 in theblock 1 transmit the monitor frames to the OpS 10 corresponding thereto(step S01).

[0054] The OpS 10, when normally functioning, transmits the responseframes responding to the monitor frames to the NEs as monitor framesenders. (step S02).

[0055] On the other hand, the sender NE, when transmitting the monitorframe, set a timer for allowing the receipt of the response frame. Thesender NE, when receiving the response frame from the OpS 10 before thetimer comes to time-out, recognizes that the OpS 10 is normal. Incontrast, the sender NE, when receiving no response frame from the OpS10 before the timer comes to time-out, recognizes that somethingabnormal occurs in the OpS 10.

[0056] Next, an operational example of the communications system 100shown in FIG. 1 will be discussed. FIG. 5 is an explanatory diagramshowing a normal operation of the system 100. Referring to FIG. 5, thefirst block information stored in the DB 11 is transferred to the OpSs20, 30, 40 from the OpS 10. The OpSs 20, 30, 40 stores the correspondingDBs 12, 13, 14 with the first block information in order to synchronizethe DBs 11, 12, 13, 14. This enables the communications system 100 tohave backup data of the DB 11 in three locations.

[0057] Similarly, the second block information stored in the DB 22 istransferred to the OpSs 10, 30, 40 from the OpS 20. The OpSs 10, 30, 40stores the corresponding DBs 21, 23, 24 with the second blockinformation in order to synchronize the DBs 21, 23, 24. This enables thecommunications system 100 to have backup data of the DB 22 in threelocations.

[0058] Likewise, the third block information stored in the DB 33 istransferred to the OpSs 10, 20, 40 from the OpS 30. The OpSs 10, 20, 40stores the corresponding DBs 31, 32, 34 with the third block informationin order to synchronize the DBs 31, 32, 34. This enables thecommunications system 100 to have backup data of the DB 33 in threelocations.

[0059] Similarly, the fourth block information stored in the DB 44 istransferred to the OpSs 10, 20, 30 from the OpS 40. The OpSs 10, 20, 30stores the corresponding DBs 41, 42, 43 with the fourth blockinformation in order to synchronize the DBs 41, 42, 43, 44. This enablesthe communications system 100 to have backup data of the DB 44 in threelocations.

[0060]FIG. 6 is a sequence diagram showing an example of the operationof synchronizing the DBs in the system 100. FIG. 6 shows the operationof the system 100 when the OpS 10 synchronizes the DBs 11, 12, 13, and14. The OpS 10, when receiving the result information from the controltarget NE (which is herein NE 1-1), rewrites the contents in the DE 11on the basis of this item of result information (steps S1˜S4: see FIG.2).

[0061] The contents in the DB 11 are rewritten, whereby differenceinformation occurs in the DE 11. The OpS 10 extracts the differenceinformation out of the DB 11, and transfers the difference informationto the OpSs 20, 30, 40 (step S4-1). The OpSs 20, 30, 40, upon receivingthe difference information from the OpS 10, rewrites the contents in theDBs 12, 13, 14 by use of the difference information (step S4-2). The DBs11, 12, 13, 14 are thereby synchronized.

[0062] On the other hand, the OpS 10, if receiving the alarm informationfrom the NE (which is herein NE 1-1) with a trouble occurred, rewritesthe contents in the DB 11 on the basis of this piece of alarminformation (steps S5˜S7: see FIG. 3).

[0063] The contents in the DB 11 are rewritten, whereby differenceinformation occurs in the DB 11. The OpS 10 extracts the differenceinformation out of the DB 11, and transfers the difference informationto the OpSs 20, 30, 40 (step S7-1).

[0064] The OpSs 20, 30, 40, upon receiving the difference informationfrom the OpS 10, rewrites the contents in the DBs 12, 13, 14 by use ofthe difference information (step S7-2). The DBs 11, 12, 13, 14 arethereby synchronized. The OpSs 20, 30, 40 in other blocks 2˜4 performthe same operation as that shown in FIG. 6.

[0065]FIG. 7 is an explanatory diagram showing a case where somethingabnormal (which will hereinafter be simply called a trouble) occurs in acertain OpS in the system 100. FIG. 8 is a sequence diagram showing anoperational example of the system 100 when the trouble happens in theOpS. FIGS. 7 and 8 show operational examples in which the trouble occursin the OpS 10 in the block 1.

[0066] Referring to FIG. 8, each of the NEs 1-1, 1-2, 1-3 in the block 1periodically transmits the monitor frame to the OpS10 and receives theresponse message to this monitor frame, thereby monitoring the operationof the OpS 10 (confirming a Keep-Alive state of the OpS 10) (see stepsS01, S02 in FIG. 4).

[0067] If the trouble (e.g., a system-down) occurs in the OpS 10 (seeFIG. 7), the OpS 10 is incapable of sending the response message to themonitor frame given from the NE to the sender NE of the monitor frame.Accordingly, the sender NE is, as shown in FIG. 8, unable to receive theresponse message before the timer comes to time-out. This is a triggerby which the sender NE judges that the trouble occurs in the OpS 10.

[0068] The NE, when detecting the trouble in the OpS 10, executes amongother NEs a process for determining a first representative NE (which maybe called a first representative NE determining process) among other NEswithin the same block 1 (step S03).

[0069] To be specific, the NE (e.g., NE 1-2) detecting the trouble ofthe OpS 10 notifies other NEs within the block embracing this NE 1-2 ofa first negotiation frame as the first representative NE determiningprocess.

[0070]FIG. 9 is a sequence diagram showing an example of the firstrepresentative determining process (step S03 including steps S03-3,S03-2) shown in FIG. 8. Referring to FIG. 9, each of the NEs 1-1, 1-2,1-3 periodically transmits the monitor frame to the OpS 10, therebymonitoring the OpS 10 (steps S01, S02). A transmission timing of themonitor frame between the NEs has a predetermined interval.

[0071] The sender NE (e.g., NE 1-2) of the monitor frame, when detectingthe trouble of the OpS 10 (step S03-0), generates the first negotiationframe (a first negotiation message), and sends this frame to other NEs(which are herein NE 1-1, 1-3) within the block 1 (step S03-1). Thefirst negotiation frame contains information (negotiation information)for negotiating among the NEs to determine which NE becomes the firstrepresentative NE.

[0072] The NEs 1-1, 1-3 receiving the first negotiation frame generatesa first negotiation response frame responding to the first negotiationframe, and transmits the first negotiation response frame to the NE 1-2as the sender NE of the first negotiation frame (step S03-2).

[0073] In this example, the first negotiation frame contains, as thenegotiation information, a piece of information indicating that thesender NE1-2 of the first negotiation frame serving as the firstrepresentative NE starts transmitting a broadcast frame BF1 (see FIG.10A). In this example also, the first negotiation response framecontains a piece of information indicating that the NEs 1-1, 1-3receiving the first negotiation frame permits the NE 1-2 to transmit thebroadcast frame BF1.

[0074] Hence, the NE 1-2 as the first representative NE, when receivingthe first negotiation response frame, executes broadcasting forsearching for a substitute OpS (step S04). The substitute OpS iscategorized as an OpS belonging to other blocks 2, 3, 4 and operating(controlling and monitoring), as a substitute for the OpS 10 with thetrouble occurred, the NEs 1-1, 1-2, 1-3 within the block 1.

[0075] Note that each NE, even when detecting the trouble of the OpSafter receiving the first negotiation frame from other NEs, does nottransmit the first negotiation frame to other NEs Accordingly, in thisexample, the NE detecting the trouble of the OpS for the first timewithin the block becomes the first representative NE.

[0076] On the other hand, one other NEs (excluding the sender NE of thefirst negotiation frame) may become the first representative NE throughthe negotiation among the NEs. For example, the NE with the minimum loadat that point of time may become the first representative NE.

[0077] Alternatively, each of the NEs has a table registered beforehandwith the information on the first representative NE. When detecting thetrouble of the OpS, the table is referred to, and the NE correspondingto the registered information on the first representative NE may becomethe first representative NE.

[0078] Referring back to FIG. 8, the first representative NE (which ishere in NE 1-2) generates a broadcast frame (or multicast frame) BF1 forsearching for a substitute OpS, and broadcasts (or multicasts) the frameBF1 to other blocks 2, 3, 4.

[0079]FIG. 10A is an explanatory diagram showing the broadcast frameBF1. The broadcast frame BF1 contains a trouble-occurred OpS number. Thetrouble-occurred OpS number is defined as information for specifying theOpS with a trouble occurred (which is herein the OpS 10). The OpSspecifying information may also be an address of the OpS.

[0080] Each of the OpSs 20, 30, 40, when receiving the broadcast frameBF1, generates a response frame BRF1 to this broadcast frame BF1, andtransmits the generated response frame BF1 to the first representativeNE (NE 1-2) by use of a address of the sender of the broadcast frame BF1(step S05).

[0081]FIG. 10B is an explanatory diagram showing the response frameBRF1. The response frame BRF1 contains a response OpS number,substitutable/non-substitutable information, CPU load information, CPUcapability information, a self-block connected NE count, a self-blockaccommodating line count, a trouble-occurred block connected NE countand a trouble-occurred block line accommodation count as parameters.Contents of these parameters are as follows:

[0082] (a) Response OpS number: A serial number (defined as informationfor specifying the OpS of the sender of the response frame) of the OpS(response OpS) that responds to the broadcast frame BF1.

[0083] (b) Substitutable/non-substitutable information: A flag forindicating whether it is possible to become the substitute OpS.

[0084] (c) CPU load information: A CPU availability factor (loadinformation).

[0085] (d) CPU capability: A CPU performance (performance information).

[0086] (e) Self-block connected NE count: The number of NEs connected tothe response OpS.

[0087] (f) Self-block accommodating line count: The number of linesaccommodated by the plurality of NEs connected to the response OpS.

[0088] (g) Trouble-occurred block connected NE count: The number of NEsconnected to the trouble-occurred OpS.

[0089] (h) Trouble-occurred block accommodating line count: The numberof lines accommodated by the plurality of NEs connected to thetrouble-occurred OpS.

[0090] Referring back to FIG. 8, the first representative NE (NE 1-2),when receiving the response frame BRF1 from each of the OpSs 20, 30, 40,executes a substitute OpS selection process by use of the parameterscontained in this response frame BRF1 (step S06).

[0091]FIG. 11 is a flowchart showing the substitute OpS selectionprocess (step S06). The first representative NE compares and collatesthe parameters obtained through the response frames BRF1, therebynarrowing down the OpSs by the substitutable/non-substitutableinformation (step S06-1), narrowing down the OpSs by the CPU loadinformation (step S06-2), narrowing down the OpSs by the response time(step S06-3), and narrowing down the OpSs by the CPUcapability/self-block connected NE count/self-block accommodating linecount/trouble-occurred block connected NE count/trouble-occurred blockline accommodating count (step S06-4). The OpS having an optimalcondition is thus selected as the substitute OpS. The sequence of stepsS06-1˜S06-4 may be arbitrarily set.

[0092] Herein, the response time is a time (a response time to thebroadcast frame BF1) till the first representative NE receives theresponse frame BRF1 from each of the OpSs 20, 30, 40 since the firstrepresentative NE has transmitted the broadcast frame BF1. Hence, thefirst representative NE, after transmitting the broadcast frame BF1,counts and records a response time from each of the OpSs 20, 30, 40 byuse of a timer incorporated into the NE itself.

[0093] Further, the OpS having the optimal condition are, for instance,an OpS with the minimum or a comparatively small load. Note that thefirst representative NE obtains information on congestion ofcommunication paths between the OpSs 20, 30, 40, and the OpS may beselected based on this item of congestion information in thisembodiment.

[0094] It is to be noted that the first representative NE may alsoselect the substitute OpS by using at least one of the parameters(a)˜(h) given above. For example, the first representative NE may selectan OpS as a substitute OpS among the OpSs, at which the response frameBRF1 arrives fastest (the substitute Ops is the OpS exhibiting theshortest response time). In this case, the OpS in the best communicationstate is selected as the substitute OpS.

[0095] Further, at leas one NE in each block has a table previouslyregistered with information on the substitute OpS. When determining thefirst representative NE, the first representative NE obtains theinformation on the substitute OpS from the table, and may also select anOpS corresponding to this item of information as the substitute OpS.

[0096] Referring again back to FIG. 8, the first representative NE, whenselecting the substitute OpS, generates and sends a substitute requestframe to the OpS corresponding to the substitute OpS (step S07). In thisexample, the OpS 30 is selected as the substitute OpS, and thesubstitute request frame is transmitted to the OpS 30.

[0097] The OpS 30, when receiving the substitute request frame startsexecuting the process as the substitute OpS (step S08), and sends back asubstitute request response frame to the substitute request frame (stepS09). The substitute request response frame contains information forindicating that the OpS (30) receiving the substitute request frameacknowledges the substitute request and functions as the substitute OpS.

[0098] When the first representative NE (1-2) receives the substituterequest response frame, each of the NEs 1-1, 1-2, 1-3 executes an OpSconnection change process in the block 1 embracing the firstrepresentative NE (step S010).

[0099]FIG. 12 is a sequence diagram showing the OpS connection changeprocess (step S010). The NE 1-2 as the first representative NE, uponreceiving the substitute request response frame from the OpS 30 as thesubstitute OpS, sends a connection change request to the NEs 1-1, 1-3 ofthe block 1 (step S010-1). The connection change request is defined as anotification for requesting the logical connection between the NEs 1-1,1-3 and the OpS to a connection with the substitute OpS (OpS 30) fromthe connection with the trouble-occurred OpS(failures-detected/failures-having operation system) (OpS 10). Theconnection change request contains a piece of substitute OpS specifyinginformation (an OpS number or address).

[0100] The first representative NE (NE 1-2), after transmitting theconnection change request, executes a disconnection process of cuttingoff the logical connection between the NE 1-2 and the OpS 10 (stepS010-2). Further, the NEs 1-1, 1-3 respectively disconnect the logicalconnections between the NEs 1-1, 1-3 and the OpS 10 (step S010-2).

[0101] The disconnection of the logical connections cuts off a relation(administrative relation) in which the OpS 10 operates (controls andmonitors) the NEs 1-1, 1-2 and 1-3. Each of the NEs 1-1, 1-2 and 1-3,even after executing the disconnection process, monitors a recovery ofthe OpS 10 and therefore periodically transmits the monitor frame to theOpS 10.

[0102] Thereafter, as shown in FIGS. 8 and 12, each of the NEs 1-1, 1-2and 1-3 executes a process of establishing the connection between the NEitself and the OpS 30 as the substitute OpS by use of the specifyinginformation on the substitute OpS, which is contained in the responseframe BRF1 or the connection change request (step S011). New logicalconnections (administrative relations) between the NEs 1-1, 1-2, 1-3 andthe OpS 30 are thereby established, and the plurality of NEs 1-1, 1-2,1-3 come under the operation of the substitute OpS.

[0103] The OpS 30 as the substitute OpS takes over, as a substituteprocess, the operation of the plurality of the NEs 1-1, 1-2 and 1-3 fromthe OpS 10. Namely, the OpS 30 operates, as by the OpS 10, the NEs 1-1,1-2 and 1-3, and updates the DBs 31 and 33 corresponding to the OpS 30itself.

[0104] With this processing, the OpS 30 substituting the OpS 10accumulates the first block information on the DB 31. Further, the OpS30, each time the OpS 30 updates the DB 31, transfers a difference(information) generated by this updating to other OpSs 20 and 40. TheDBs 21, 31 and 41 accumulating with the first block information arethereby initialized.

[0105] Next, an operational example of the communications system 100when the trouble-occurred OpS (failures-detected OpS) is restored, willbe explained.

[0106]FIG. 13 is a sequence diagram showing an operation of the system100 when the OpS is restored in the operational example shown in FIGS. 7and 8. FIG. 14 is a sequence diagram showing a second representative NEdetermination process (step S022).

[0107] Each of the NEs 1-1, 1-2, 1-3 in the block 1, even after thedisconnection process (step S010-2), periodically sends the monitorframe to the OpS 10, and accepts a response message to this monitorframe (step S01). With this acceptance, each of the NEs 1-1, 1-2, 1-3monitors a recovery of the OpS 10. On the other hand, the OpS is, whenrecovered from the troubling state (step S021), capable of sending theresponse frame to the monitor frame.

[0108] Each of the NEs 1-1, 1-2, 1-3, upon receiving the response framefrom the OpS 10, recognizes that the OpS 10 has recovered from thetroubling state, and executes the second representative NE determinationprocess (step S022). Namely, each of the NEs 1-1, 1-2, 1-3, whendetecting the recovery of the OpS 10 (step S022-0), transmits a secondnegotiation frame (a second negotiation message) to other NEs in theblock 1 (step S022-1).

[0109] In the example shown in FIG. 14, the NE 1-2 detects the recoveryof the OpS 10 and transmits the second negotiation frame to other NEs1-1, 1-3. The second negotiation frame contains information fornegotiating (negotiation information) among the NEs to determine whichNE becomes the second representative NE.

[0110] The NEs 1-1, 1-3 receiving the second negotiation frame generatea second negotiation response frame to the second negotiation frame, andsend this response frame to the NE 1-2 (step S022-2). In this example,the second negotiation frame contains information indicating that theNE1-2 as a sender of the second negotiation frame becomes the secondrepresentative NE. A second negotiation response frame containsinformation indicating that the NEs 1-1, 1-3 receiving the secondnegotiation frame acknowledge that the NE 1-2 becomes the secondrepresentative NE.

[0111] Accordingly, the NE 1-2 as the second representative NE, uponreceiving the second negotiation response frame, executes broadcastingfor searching for a restoration-process-assigned OpS (step S023). Therestoration-assigned OpS is categorized as an OpS in charge of a processof restoring the DBs 11, 21, 31, 41 in the block 1.

[0112] Note that each NE, when receiving the second negotiation framefrom other NEs, does not send the second negotiation frame to other NEseven if detecting the recovery of the OpS after receiving the secondnegotiation frame. Hence, in this example, the NE, which is the first todetect the recovery of the OpS in the block, becomes the secondrepresentative NE.

[0113] In contrast, one of other NEs (excluding the sender NE of thesecond negotiation frame) may become the second representative NE by thenegotiation among these NEs. The alternative is such that theinformation on the second representative NE is registered beforehand inthe respective NEs in each block, and, when the recovery of the OpS isdetected, the NE corresponding to the registered information about thesecond representative NE may become the second representative NE.

[0114] The second representative NE (which is herein NE 1-2) generates abroadcast frame (or multicast frame) BF2 for searching for a restorationtarget OpS, and broadcasts (multicasts) this frame BF2 to other blocks2, 3, 4 (step S023)

[0115]FIG. 15A is an explanatory diagram showing the broadcast frameBF2. The broadcast frame BF contains a restoration target OpS number.The restoration target OpS number is defined as a piece of informationfor specifying an OpS (which is herein a restoration target OpS 10)recovered from the troubling state. The OpS specifying information mayalso be an OpS address.

[0116] Referring back to FIG. 13, each of the OpSs 20, 30, 40, whenreceiving the broadcast frame BF2, generates a response frame BRF2 tothis broadcast frame BF2, and transmits the generated response frame BF2to the second representative NE (1-2) by use of an address of the senderof the broadcast frame BF2 (step S024).

[0117]FIG. 15B is an explanatory diagram showing the response frameBRF2. The response frame BRF2 has substantially the same parameters asthose of the response frame BRF1 except that thesubstitutable/non-substitutable information is replaced withrestoration-assignable/non-assignable information. Therestoration-assignable/non-assignable information is a flag forindicating whether it is possible to become the restoration-assignedOpS.

[0118] Referring back to FIG. 13, the second representative NE (1-2),when receiving the response frame BRF2 from each of the OpSs 20, 30, 40,executes a process of selecting the restoration-assigned OpS by use ofthe parameters contained in the response frame BRF2 (step S025).

[0119]FIG. 16 is a flowchart showing the restoration-assigned OpSselection process (step S025). The second representative NE executessubstantially the same process as the substitute OpS selection process(step S06) by use of the parameters obtained through the response frameBRF2 given from each of the OpSs 20, 30, 40, thereby selecting ordetermining the restoration-assigned OpS.

[0120] Namely, the second representative NE narrows down the OpSs by therestoration-assignable/non-assignable information (step S025-1), narrowsdown the OpSs by the CPU load information (step S025-2), narrows downthe OpSs by the response time (step S025-3), and narrows down the OpSsby the CPU capability/self-block connected NE count/self-blockaccommodating line count/trouble-occurred block connected NEcount/trouble-occurred block line accommodating count (step S025-4). TheOpS having an optimal condition is thus selected or determined as therestoration-assigned OpS. Note that a variety of methods explained sofar by way of the substitute OpS selection method can be applied to amethod of selecting the restoration-assigned OpS. Further, it ispreferable that the second representative NE be structured to select anOpS, as the restoration-assigned OpS, different from the substitute OpS.This contrivance prevents both of a load concentration on one single OpSand a decline of performance of the OpS.

[0121] Referring again back to FIG. 13, the second representative NE,when selecting the restoration-assigned OpS, generates a DB restorationrequest frame and transmits the OpS serving as the restoration-assignedOpS (step S026). In this example, the OpS 20 is selected as therestoration-assigned OpS, and the DB restoration request frame istransmitted to the OpS 20.

[0122] The OpS 20, upon receiving the DB restoration request frame,executes a DB restoration process as the restoration-assigned OpS (stepS028). Namely, the OpS 20 reads first through fourth block informationaccumulated in the DBs 21, 22, 23, 24, and transfers the same blockinformation to the OpS 10. The OpS 10 stores the DBs 11, 21, 31, and 41with the first to fourth block information received from the OpS 20. Thecontents accumulated in the DBs 11, 12, 13, 14 in the block 1 arethereby synchronized with the plurality of DBs in other blocks 2, 3, and4. Thus, the DBs 11, 12, 13 and 14 in the block 1 are restored.

[0123] The OpS 20, when finishing the DB restoration process, transmitsa DB restoration process end notification to the NE 1-2 as the secondrepresentative NE (step s029). The second representative NE, whenreceiving the DB restoration process end notification, transmits asubstitute end notification to the OpS 30 as the substitute OpS (stepS030).

[0124] The OpS 30, upon receiving the substitute end notification,executes a substitute end process (step S031). That is, the OpS 30finishes the process for operating the NEs 1-1, 1-2, 1-3. Thereafter,the OpS 30 transmits a response notification to the substitute endnotification to the NE 1-2 as the second representative NE (step S032).

[0125] The NE 1-2 as the second representative NE, upon receiving theresponse notification, executes the OpS connection change process (stepS033) FIG. 17 is a sequence diagram showing the OpS connection changeprocess (step S033). The NE 1-2, when receiving the responsenotification from the OpS 30, sends a connection change request to theNEs 1-1, 1-3, thereby requesting the NEs 1-1, 1-3 to change theconnection relationship between the NEs 1-1, 1-3 and the OpS to theconnection with the previous OpS (OpS 10) from the connection with thesubstitute OpS (OpS 30) (step s033-1).

[0126] The NE 1-2, transmitting the connection change request, executesa process of cutting off the connection relationship between the NE 1-2and the OpS 30 (step S033-2). Further, the NEs 1-1, 1-3, when receivingthe connection change request, cut off the connection relationshipbetween NEs 1-1, 1-3 and the OpS 30 (step S033-2). Thus, the NEs 1-1,1-2, 1-3 get released from under the operation of the substitute OpS.

[0127] Thereafter, the NEs 1-1, 1-2, 1-3 execute the process ofestablishing the connections between the NEs and the OpS 10 (step S034).With this process executed, a state of the block 1 reverts to the statebefore the trouble occurs in the OpS 10.

[0128] According to the communications system 100 in the embodiment ofthe present invention, in each block (defined as a group consisting ofthe OpS and the NEs operated by this OpS), when each NE detects thetrouble in the OpS by monitoring the OpS, the first representative NE isdetermined among the plurality of NEs in this block. The firstrepresentative NE selects the substitute OpS, and sends the substituterequest (corresponding to an [operation request]) to the selectedsubstitute OpS. Then, the plurality of NEs (that are all the NEs in theblock including the OpS with its trouble detected) under the operationof the OpS with the trouble detected, come under the operation of thesubstitute OpS.

[0129] Thus, according to the communications system 100, if a certainOpS (administrative system) is incapable of functioning due to itstrouble, other OpS as the substitute OpS takes over the operation of theNEs, thereby backing up the OpS.

[0130] This backup process is actualized by the NE that monitors the OpSand executes the first representative NE determination process, thesubstitute OpS selection process, the substitute request transmissionprocess and the process of establishing the connection to the substituteOpS. Thus, the backup process is actualized the NE as a primeimplementer.

[0131] Accordingly, unlike the prior art, there is no necessity forproviding the host OpS in the communications system 100, and it istherefore feasible to restrain a rise in the operating cost for thecommunications system 100. Further, there is no possibility in which aload on the OpS increases and the OpS performance decreases due tomutual monitoring between the OpSs.

[0132] Moreover, the first representative NE dynamically selects thesubstitute OpS by using the response frame BRF1 and the information (theparameters (a)˜(h)) contained in this response frame BRF1. For example,the substitute OpS is selected based on the CPU load information,whereby the OpS exhibiting the minimum load at this point of time isselected. The alternative is that the substitute OpS is selected basedon the response time, whereby an OpS exhibiting the best communicationstate (traffic state) (the highest throughput) is selected. Thus, theoptimal OpS is selected as the substitute OpS, and the substitute OpSexecutes the substitute process. The communications system 100 isthereby well operated.

[0133] Further, the substitute OpS, in the substitute process,accumulates on its own database the operation information (the firstblock information in the illustrated example) on the NEs coming newlyunder the operation of the substitute OpS itself, and transfers theoperation information to other OpSs, thereby actualizing thesynchronization of the first block information between the databasesexcluding the database corresponding to the OpS with the troubledetected.

[0134] As described above, after the substitute OpS has been determined,the logical connection of the NEs in the block embracing the OpS withits trouble occurred, is changed to the connection with the substituteOpS. Hence, the databases of the OpS in the operation block are held bythe OpSs in other blocks, and the change difference information istransferred to the OpSs in other blocks, whereby several OpSs have thedatabases at all times. This architecture actualizes that the OpSsperform the backup function each other.

[0135] Thereafter, if the OpS with the trouble detected is recovered,the second representative NE is determined. The second representative NEselects the restoration-assigned OpS, and the restoration process isexecuted between the restoration-assigned OpS and the OpS with itsrecovery detected, and the plurality of databases accommodated in theOpS with its recovery detected are restored. Then, the substituteprocess is finished, the plurality of NEs operated by the substituteprocess get released from under the operation of the substitute OpS andcome (return to) under the operation of the OpS with the recoverydetected. The state of the communications system 100 thereby reverts tothe state (conceived optimal) before the trouble occurs in the OpS.

[0136] The present invention having the architecture described above canexhibit the following effects.

[0137] <1> If the trouble occurs in the OpS, the optimal OpS isdynamically selected corresponding to the load on each OpS and the stateof the monitor control network, and the logical connection of the NEsoperated by the OpS with the trouble occurred is changed to theconnection with the substitute OpS. This actualizes the exact recoveryof the monitor control network (the communications system) under theminimum influence upon the monitor control system (the communicationssystem).

[0138] <2> The substitute OpS determination process is actualized by thecommunications device (NE: network element) as the monitor/controltarget device, thereby actualizing the reduction in the load upon eachof the OpSs.

[0139] <3> There is no necessity for separately installing and operatingthe host OpS in order to confirm the normality of each OpS, therebyactualizing the reduction in the operating cost.

[0140] <4> When the OpS is recovered from the trouble, the optimal OpSin charge of restoring the DBs is dynamically selected corresponding tothe load upon each OpS and the state of the monitor control network, andthe restoration process of the DBs of the OpS recovered from the troubleis actualized under the minimum influence on the monitor control system(the communications system).

[0141] Further, according to this embodiment, the following architecturemay be added. To be specific, when configuring the communications system100 in the embodiment, if the OpS and the NE are booted at the sametime, a startup time of the OpS might be longer than a startup tome ofthe NE.

[0142] In this case, eve when the NE sends the monitor frame to the OpS,the OpS does not yet get ready for transmitting the response frame andis therefore unable to send the response frame to the NE. In thisinstance, the NE might mistakenly detect the trouble in the OpS. To givea troubleshooting scheme, the NE implements a function (a frametransmission restraining function) of restraining the first negotiationframe (the negotiation message) from being transmitted to other NEs andrestraining the broadcast frame BF1 from being sent to other OpSs till astartup notification is received from the OpS even when detecting thetrouble in the OpS. A processor incorporated into the NE executes apredetermined program, whereby this function can be actualized.

[0143]FIG. 18 is an explanatory sequence diagram showing the frametransmission restraining function. For example, when configuring thecommunications system 100, it is assumed that the NE and the OpS arestarted up (booted) simultaneously (S101, S201). The NE, upon booting,gets ready for transmitting the monitor frame to the OpS, while the OpS,upon booting, gets ready for sending the response frame back to the NE.

[0144] In this case, if the NE comes to a completion of the preparationfaster than OpS, the NE starts transmitting periodically the monitorframe to the OpS. Just when the NE comes to the completion of thepreparation, however, a trouble detection inhibiting flag (a negotiationmessage restraining message), set in the NE, for restraining(inhibiting) the detection of the trouble in the OpS, is in an ON-state(wherein the trouble detection (the transmission of the firstnegotiation frame) is inhibited).

[0145] Therefore, the NE transmits the monitor frame to the OpS (S01)and, even if unable to receive the response frame within a predeterminedperiod, does not detect the trouble in the OpS. Thereafter, when the OpScompletes the preparation (S202), the OpS sends acompletion-of-preparation notification (a completion-of-startupnotification) to the NE (S203).

[0146] The NE, when receiving the completion-of-preparation notificationfrom the OpS, transmits to the OpS a notification of response thereto(S103), and sets the trouble detection inhibition flag OFF (in a statethat permits the detection of the trouble) (S104). With this setting,the NE, if unable to receive the response frame within a predeterminedperiod since the monitor frame has been sent, detects the trouble in theOpS and transmits the first negotiation frame. On the other hand, theOpS, after transmitting the completion-of-preparation notification,sends back the response frame with respect to the monitor frame givenfrom the NE. This architecture prevents the NR from mistakenly detectingthe trouble in the OpS.

What is claimed is:
 1. A backup system for an operation system in acommunications system, comprising: a plurality of operation systemsconnected to each other via a network; and a plurality of networkelements operated by the plurality of operation systems, wherein each ofthe operation systems operates at least one of the plurality of networkelements, each of the network elements monitors the operation systemthat operates the network element itself and detects failures in thisoperation system, when the failures are detected, if thefailures-detected operation system operates a plurality of networkelements, a representative network element is determined among theplurality of network elements under the failures-detected operationsystem, the representative network element selects a substituteoperation system among the other operation systems and transmits anoperation request to the substitute operation system, and each of theoperation systems, when receiving the operation request, as thesubstitute operation system, operates the plurality of network elementsunder the failures-detected operation system.
 2. A backup system for anoperation system in a communications system according to claim 1,wherein the representative network element respectively transmits aframe for selecting the substitute operation system to the otheroperation systems before sending the operation request, each of theother operation systems, when receiving the frame, transmits a responseframe to the frame to the representative network element, and therepresentative network element receives the response frames respectivelyfrom the other operation systems, and selects, as the substituteoperation system, the other operation system detected as a sender of theresponse frame received first by the representative communicationsystem.
 3. A backup system for an operation system in a communicationssystem according to claim 1, wherein the representative network elementrespectively transmits a frame for selecting the substitute operationsystem to the other operation systems before sending the operationrequest, each of the other operation systems, when receiving the frame,transmits a response frame to the frame to the representative networkelement, and the representative network element receives the responseframes respectively from the other operation systems, and selects thesubstitute operation system by use of information contained in theseresponse frames.
 4. A backup system for an operation system in acommunications system according to claim 1, wherein each of theoperation systems has a plurality of databases correspondingrespectively to the plurality of operation systems, updates the databasecorresponding to the operation system itself by use of informationobtained by operating at least one network element under the operationsystem itself, transfers difference information generated by theupdating to the all other operation systems, if receiving the differenceinformation from the other operation system, updates the databasecorresponding to the other operation system by use of the receiveddifference information, further updates, if operating as a substituteoperation system at least one network element under thefailures-detected operation system, the database corresponding to thefailures-detected operation system by use of the information obtained byoperating the at least one network element, and transfers differenceinformation generated by the updating to the all other operation systemsor the other operation systems excluding the failures-detected operationsystem.
 5. A backup system for an operation system in a communicationssystem according to claim 1, wherein the network element, which is thefirst to detect the failures in an operation system among a plurality ofnetwork elements under this operation system, becomes the representativenetwork element.
 6. A backup system for an operation system in acommunications system according to claim 2, wherein each of the networkelements, when detects the operation system, if the failures-detectedoperation system operates only the network element itself, transmits anoperation request to a substitute operation system selected from theother operation systems, and each of the operation systems, whenreceiving the operation request, operates as the substitute operationsystem the sender network element of the operation request.
 7. A backupsystem for an operation system in a communications system according toclaim 1, wherein the plurality of network elements that the operationsystem is changed, while being operated by the substitute operationsystem, monitor the failures-detected operation system, get released, ifany one of the network elements detects a recovery of thefailures-detected operation system, from under the operation of thesubstitute operation system, and return to under the operation of thefailure-detected operation system.
 8. A backup system for an operationsystem in a communications system according to claim 4, wherein theplurality of network elements that the operation system is changed,while being operated by the substitute operation system, respectivelymonitor the failures-detected operation system, determine, when any oneof the plurality of network elements detects a recovery of thefailures-detected operation system, a second representative networkelement from the plurality of network elements, the secondrepresentative network element selects, from the plurality of otheroperation systems, a restoration-assigned operation system assigned aprocess of restoring the plurality of databases included in thefailures-detected operation system, and transmits a restoration requestfor restoring the databases of targets to the restoration-assignedoperation system, the restoration-assigned operation system, whenreceiving the restoration request, transfers contents accumulated in theplurality of databases included in the restoration-assigned operationsystem to the failures-detected operation system, and thefailure-detected operation system, when receiving the accumulatedcontents from the restoration-assigned operation system, updatesrespectively the plurality of databases under itself by use of theaccumulated contents.
 9. A backup system for an operation system in acommunications system according to claim 8, wherein the secondrepresentative network element, before transmitting the restorationrequest, transmits a frame for selecting the restoration-assignedoperation system to the other operation systems, each of the otheroperation systems, when receiving the frame, respectively transmits aresponse frame corresponding to the frame to the second representativenetwork element, and the second representative network element receivesthe response frames respectively from the other operation systems, andselects, as a restoration-assigned operation system, the other operationsystem detected as a sender of the response frame received first by thesecond representative communication system.
 10. A backup system for anoperation system in a communications system according to claim 8,wherein the second representative network element, before transmittingthe restoration request, transmits a frame for selecting therestoration-assigned operation system to the other operation systems,each of the other operation systems, when receiving the frame,respectively transmits response frame corresponding to the frame to thesecond representative network element, and the second representativenetwork element receives the response frames respectively from the otheroperation systems, and selects a restoration-assigned operation systemby use of information contained in these response frames.
 11. A backupsystem for an operation system in a communications system according toclaim 8, wherein the second representative network element selects, as arestoration-assigned operation system, the operation system not selectedas the substitute operation system, from the other operation systems.12. A backup system for an operation system in a communications systemaccording to claim 8, wherein the network element, which is the first todetect the recovery of the operation system among the plurality ofnetwork elements monitoring the failures-detected operation system,becomes the second representative network element.
 13. A backup systemfor an operation system in a communications system according to claim 1,wherein each of the network elements transmits a monitor frame to theoperation system that operates the network element itself, monitors theoperation system by receiving a response frame to this monitor framefrom the operation system, and detects failures in the operation systemonly in a case where the response frame is not received before an elapseof a predetermined period since the monitor frame has been transmitted,and where a notification showing a completion of a preparation forsending the response frame has already been received from the operationsystem.
 14. A backup method for an operation system in a communicationssystem comprising: a plurality of operation systems connected to eachother via a network; and a plurality of network elements operated by theplurality of operation systems, the method comprising: a step ofoperating each of the operation systems to operate at least one of theplurality of network elements; a step of operating the network elementto monitor the operation system that operates the network elementitself, then, if the operation system operate the plurality of networkelements including the network element itself when detecting a troublein the operation system, and determine a representative network elementrepresentative of the plurality of network elements; a step of operatingthe representative network element to select, from among a plurality ofother operation systems, a substitute operation system for operating theplurality of network elements as a substitute for the operation systemwith the trouble detected, and transmit a operation request foroperating the plurality of network elements to the selected substituteoperation system; a step of operating the plurality of network elements,after the operation request has been transmitted, to come under theoperation of the substitute operation system; and a step of operatingeach of the operation systems, when receiving the operation request, tooperate as the substitute operation system the plurality of networkelements.
 14. A backup method for an operation system in acommunications system, comprising a plurality of operation systemsconnected to each other via a network, and a plurality of networkelements operated by the plurality of operation systems, the methodcomprising steps of: operating each of the operation systems operates atleast one of the plurality of network elements; operating each of thenetwork elements monitors the operation system that operates the networkelement itself and detects failures in this operation system, when thefailures are detected, if the failures-detected operation systemoperates a plurality of network elements, a representative networkelement is determined among the plurality of network elements under thefailures-detected operation system, the representative network elementselects a substitute operation system among the other operation systemsand transmits an operation request to the substitute operation system;and operating each of the operation systems, when receiving theoperation request, as the substitute operation system, operates theplurality of network elements under the failures-detected operationsystem.
 15. A backup method for an operation system in a communicationssystem according to claim 14, wherein the representative network elementrespectively transmits a frame for selecting the substitute operationsystem to the other operation systems before sending the operationrequest, each of the other operation systems, when receiving the frame,transmits a response frame to the frame to the representative networkelement, and the representative network element receives the responseframes respectively from the other operation systems, and selects, asthe substitute operation system, the other operation system detected asa sender of the response frame received first by the representativecommunication system.
 16. A backup method for an operation system in acommunications system according to claim 14, wherein the representativenetwork element respectively transmits a frame for selecting thesubstitute operation system to the other operation systems beforesending the operation request, each of the other operation systems, whenreceiving the frame, transmits a response frame to the frame to therepresentative network element, and the representative network elementreceives the response frames respectively from the other operationsystems, and selects the substitute operation system by use ofinformation contained in these response frames.
 17. A backup method foran operation system in a communications system according to claim 14,wherein each of the operation systems has a plurality of databasescorresponding respectively to the plurality of operation systems,updates the database corresponding to the operation system itself by useof information obtained by operating at least one network element underthe operation system itself, transfers difference information generatedby the updating to the all other operation systems, if receiving thedifference information from the other operation system, updates thedatabase corresponding to the other operation system by use of thereceived difference information, further updates, if operating as asubstitute operation system at least one network element under thefailures-detected operation system, the database corresponding to thefailures-detected operation system by use of the information obtained byoperating the at least one network element, and transfers differenceinformation generated by the updating to the all other operation systemsor the other operation systems excluding the failures-detected operationsystem.
 18. A backup method for an operation system in a communicationssystem according to claim 14, wherein the network element, which is thefirst to detect the failures in an operation system among a plurality ofnetwork elements under this operation system, becomes the representativenetwork element.
 19. A backup method for an operation system in acommunications system according to claim 15, wherein each of the networkelements, when detects the operation system, if the failures-detectedoperation system operates only the network element itself, transmits anoperation request to a substitute operation system selected from theother operation systems, and each of the operation systems, whenreceiving the operation request, operates as the substitute operationsystem the sender network element of the operation request.
 20. A backupmethod for an operation system in a communications system according toclaim 14, wherein the plurality of network elements that the operationsystem is changed, while being operated by the substitute operationsystem, monitor the failures-detected operation system, get released, ifany one of the network elements detects a recovery of thefailures-detected operation system, from under the operation of thesubstitute operation system, and return to under the operation of thefailure-detected operation system.
 21. A backup method for an operationsystem in a communications system according to claim 17, wherein theplurality of network elements that the operation system is changed,while being operated by the substitute operation system, respectivelymonitor the failures-detected operation system, determine, when any oneof the plurality of network elements detects a recovery of thefailures-detected operation system, a second representative networkelement from the plurality of network elements, the secondrepresentative network element selects, from the plurality of otheroperation systems, a restoration-assigned operation system assigned aprocess of restoring the plurality of databases included in thefailures-detected operation system, and transmits a restoration requestfor restoring the databases of targets to the restoration-assignedoperation system, the restoration-assigned operation system, whenreceiving the restoration request, transfers contents accumulated in theplurality of databases included in the restoration-assigned operationsystem to the failures-detected operation system, and thefailure-detected operation system, when receiving the accumulatedcontents from the restoration-assigned operation system, updatesrespectively the plurality of databases under itself by use of theaccumulated contents.
 22. A backup method for an operation system in acommunications system according to claim 21, wherein the secondrepresentative network element, before transmitting the restorationrequest, transmits a frame for selecting the restoration-assignedoperation system to the other operation systems, each of the otheroperation systems, when receiving the frame, respectively transmits aresponse frame corresponding to the frame to the second representativenetwork element, and the second representative network element receivesthe response frames respectively from the other operation systems, andselects, as a restoration-assigned operation system, the other operationsystem detected as a sender of the response frame received first by thesecond representative communication system.
 23. A backup method for anoperation system in a communications system according to claim 21,wherein the second representative network element, before transmittingthe restoration request, transmits a frame for selecting therestoration-assigned operation system to the other operation systems,each of the other operation systems, when receiving the frame,respectively transmits response frame corresponding to the frame to thesecond representative network element, and the second representativenetwork element receives the response frames respectively from the otheroperation systems, and selects a restoration-assigned operation systemby use of information contained in these response frames.
 24. A backupmethod for an operation system in a communications system according toclaim 21, wherein the second representative network element selects, asa restoration-assigned operation system, the operation system notselected as the substitute operation system, from the other operationsystems.
 25. A backup method for an operation system in a communicationssystem according to claim 21, wherein the network element, which is thefirst to detect the recovery of the operation system among the pluralityof network elements monitoring the failures-detected operation system,becomes the second representative network element.
 26. A backup methodfor an operation system in a communications system according to claim14, wherein each of the network elements transmits a monitor frame tothe operation system that operates the network element itself, monitorsthe operation system by receiving a response frame to this monitor framefrom the operation system, and detects failures in the operation systemonly in a case where the response frame is not received before an elapseof a predetermined period since the monitor frame has been transmitted,and where a notification showing a completion of a preparation forsending the response frame has already been received from the operationsystem.